Effects of Antibodies to Estradiol-17β and to Progesterone on Nidation and Pregnancy in Rats

Abstract

The effects of the administration to pregnant rats of antibodies to progesterone (anti-P) and to estradiol-17β (anti-E2) were studied. When given prior to nidation, anti-E2 or anti-P delayed implantation by 24–48 hr, as evidenced by the presence of free intrauterine ova on days 6 or 7. Furthermore, treatment with anti-P on day 3 or anti-E2 on day 4 had a long-term deleterious effect on the development of the embryos, as shown by a marked reduction in the number of implantation sites on days 9 and 17. Treatment with anti-P on day 11, but not on days 7, IS, or 19, resulted in complete resorption of the implantation sites in all animals. Likewise, treatment with anti-E2 on day 11 produced complete resorption, but only in 40% of the animals. These experiments confirm the need for progesterone followed by estrogens as a prerequisite for implantation. They also offer direct evidence that gestational viability on day 11 is dependent upon the presence not only of progesterone, but also of estrogens. (Endocrinology90: 1133, 1972)